1. Technical Field
The purpose of this invention is an electrical connection between two faces of a substrate and a process for making this connection. Its applications include the manufacture of electronic components or circuits or devices necessitating electrical connections like magnetic heads or sensors.
2. State of Prior Art
Document FR-A-2 637 161 describes a process for making electrical connections through a substrate. This process is illustrated in FIGS. 1A, 1B and 1C attached. An insulating layer 12 is deposited on a substrate 10 and the back face of the substrate is scanned at a defined pitch by a laser beam with an appropriate wavelength. The laser radiation is absorbed by the substrate and causes local abrasion of the substrate. When the entire thickness of the substrate has been abraded, radiation reaches the insulating layer 12 which is transparent to the chosen radiation. It remains intact and therefore forms a bottom for holes perforated in the substrate and which are consequently not through holes. Thermal oxidation is then carried out, particularly creating an insulating layer 14 on the wall of holes and on the back face of the substrate (FIG. 1A).
A conducting layer 16 is then deposited that coats the sides and the bottom of the holes. An etching technique is then used to remove part of the insulating layer 12 covering the front face of the conducting layer to create an opening 18 (FIG. 1B).
An electrical contact is then made on the metallic layer 16 through a conducting pad 18 (FIG. 1C). The electrical connection between the front face and the back face of the substrate is then made through the metallic material of the pad 18 and the metallic layer 16. The next step is to use traditional means to make the electrical circuit on the front face of the substrate.
This type of process has at least two disadvantages:
due to the presence of holes in the substrate, particular precautions have to be taken during some operations related to manufacturing of the circuit, such as spreading of resin, cleaning of parts, etc.;
the presence of a metallic material in the holes different from the substrate creates stresses and deformations during steps in which temperatures higher than the ambient temperature are necessary; these same stresses and deformations are very harmful during operation of the component at high temperature.
The purpose of this invention is to overcome these disadvantages, by avoiding the presence of holes and reducing differences in nature between different materials.
Document EP-0 926 726 describes a process for making an electronic circuit in which a trench is perforated in a stack formed from a semi conducting substrate, an insulating layer and a dielectric layer. This trench is filled with an oxide. The next step is to drill an opening that is filled with metal. The metallic cylinder makes the connection, as in a normal technique rather than a stack of layers, since the stack of layers comprises two insulating layers.
The abstract for Japanese patent vol. 1995, No. 02, Mar. 31, 1995 (and JP 06 310 489) describes an etching process for a semi conducting substrate. The objective is not to create a permanent connection but to simplify an electrolytic process by enabling the lower face of a substrate immersed in an electrolyte to be raised to an appropriate potential.
The abstract for Japanese patent, vol. 009, No. 251 (E-348), Oct. 8, 1985 (and JP 60 10 1945) describes a process for making a semi conducting component in a substrate and for isolating this component from the rest of the substrate. Therefore, the objective is not to make a connection between one face of the substrate and the other face.
Document EP-A-0 974 817 describes a circuit card for a detector, comprising a cylindrical insulating region formed throughout the thickness of the substrate, the insulation flush with the surface of the substrate.
The invention proposes an electrical connection (called xe2x80x9cviaxe2x80x9d conductor) in which the substrate is a conductor (or semiconductor), this conducting property being used to make the connection. It will be observed that in prior art that has been described, if a conducting substrate is used, this conductivity will not always be advantageous since the connection would always be made through an add-on material (layer 16) that is different from the substrate.
According to the invention, the substrate itself will be used as an electrical connection means between the two faces. The part of the substrate that makes this connection must naturally be electrically insulated from the rest of the substrate. This insulation function is done by at least one trench (that can also be called a partition or wall), extending throughout the thickness of the substrate and completely surrounding part of the substrate forming the connection. This (or these) trench(es) must be at least partly filled in to achieve mechanical strength of the entire substrate.
Specifically, the purpose of this invention is a process for making an electrical connection between two faces of a substrate comprising the following operations:
the starting point is a conducting or semi conducting substrate,
at least one electrically insulating trench completely surrounding part of the substrate is made throughout the thickness of the substrate, this trench being filled in over at least part of its depth,
a first conducting means is deposited on one of the faces of the substrate, this means being in electrical contact with the substrate over the part completely surrounded by the trench,
this process being characterized in that:
a first groove is formed starting from a first face of the substrate, and this first groove is filled in by at least one insulating material,
the substrate is thinned until it has the required thickness,
a second conducting means is formed on the thinning face of the thinned substrate facing the part of the substrate that is completely surrounded by the groove,
a second groove is formed starting from the thinning face of the thinned substrate, facing the first groove and opening up onto the material filling the first groove,
said electrical connection thus being set up by said part of the substrate completely surrounded by the trench and by the first and second conducting means.
Another purpose of this invention is an electrical connection obtained by the process defined above. This connection comprises:
at least one electrically insulating trench extending throughout the thickness of the substrate and completely surrounding part of the substrate, this trench being filled in over at least part of its depth,
a first conducting means on one of the faces of the substrate, this means being in electrical contact with the substrate in the part completely surrounded by the trench,
a second conducting means on the other face of the substrate, in electrical contact with the substrate in said part completely surrounded by the trench,
said connection thus being set up by said part of the substrate completely surrounded by the trench and by the first and second conducting means,
this electrical connection being characterized in that:
the filled in part of the trench comprises a first groove formed in the substrate starting from a first face of the substrate, an electrically insulating material filling in this first groove and a second groove formed in the substrate, starting from a second face of the substrate, this second groove having a bottom opening up into the filled in part of the trench.
The trench may be formed from two grooves facing each other and each formed from the opposite sides of the substrate. One of the grooves, or possibly both, are filled in.
According to one embodiment, the filled in part of the trench comprises a first groove etched in the substrate starting from a first face of the substrate, an electrically insulating material filling in this first groove.
According to another embodiment, the wall of the first groove is covered by an insulating layer and the groove is filled in by another material. This other material may be electrically conducting or semi-conducting; preferably, the coefficient of expansion of this material is similar to the coefficient of expansion of the substrate.
This trench can be made by etching two communicating grooves starting from the two faces of the substrate and filling in at least one of them or making a single groove and thinning the other face of the substrate as far as the said groove.
It is also possible to make several concentric or non-concentric trenches, for example two, one on the inside and one on the outside.
In the above definitions, the xe2x80x9cfirstxe2x80x9d and xe2x80x9csecondxe2x80x9d faces may be the xe2x80x9cfrontxe2x80x9d and xe2x80x9cbackxe2x80x9d faces of the substrate or the xe2x80x9cbackxe2x80x9d and xe2x80x9cfrontxe2x80x9d faces, since these names are conventional and have no limitative nature.